1. Field of the Invention
The present invention relates to an image processing technology, particularly to a technology of embedding a secret message into a PNG (Portable Network Graphics) image.
2. Description of the Related Art
In the age of network, various communications are highly involved with the Internet. And so, various files, such as text, voices and images, are transmitted via networks.
However, network communication lacks sufficient security. Thus, secret information is encrypted before transmission, and the recipient decrypts the encrypted information to obtain the original information. Although encryption can increase security of information transmission, encrypted data is similar to random code and likely to be recognized and depredated. Therefore, there is a steganographic technology, which increases information security via hiding secret information into a cover file to yield a stego-file. The stego-file is transmitted to the recipient, and the recipient decrypts the stego-file to retrieve the secret information. The steganographic technology can greatly reduce the probability of arousing suspicion. The information hidden in a cover file is less likely to be recognized than encrypted information.
A U.S. patent No. 20067035700 disclosed a technology to hide a secret message into an audio file, wherein the secret message is embedded in the audio file via varying the magnitude of the power spectrum at perceptual holes. However, such a technology results in distortion to the original audio content. A U.S. patent No. 20036557103 disclosed a technology using an image file to carry a secret message, wherein the secret message is encoded with an error correcting code and then embedded into images according to a random sequence generated by a key. However, such a technology can only hide a limited amount of secret information. A U.S. patent No. 20107751548 disclosed a technology hiding secret messages in firmware images. However, firmware images are less likely to obtain. A Taiwan patent No. 468337 disclosed a technology using interleaving, convolutional encoding and the relationship of the surrounding pixels to hide secret messages. A Taiwan patent No. 201025225 disclosed a technology, which compresses secret messages and directly embeds the compressed data into host images. However, the abovementioned two prior arts cause distortion to host images more or less.
After reviewing the abovementioned conventional steganographic technologies, the Inventors integrate the secret sharing technique with the alpha channel supported by the image format of PNG to develop a method for embedding a secret message into PNG images.